At least a few investors believe 49ers tight end Vernon Davis will have a lucrative career.

An unusual stock tied to Davis' earning potential gained $2 to close at $12 in its trading debut Monday. Only 496 shares had traded as of Monday afternoon.

Fantex Brokerage Services said last week it would offer 421,000 shares of the tight end at a price of $10 a share. Those who wanted to buy shares were required to place a reservation and fund their accounts before Monday's initial public offering.

The 20 percent gain represents a vote of confidence in Davis, an eight-year NFL veteran.

The value of the tracking stock offered by Fantex will depend on Davis' ability to sign a big contract after his current deal with the 49ers expires in 2015.

In October, Fantex agreed to buy a 10 percent interest in Davis' future earnings for $4 million. The company collects that percentage from Davis' playing contract, endorsements and any other money he makes, including post-career income like a broadcasting deal.

"We think it's historic, not just from a sports perspective, but from a finance perspective, too,'' Fantex CEO Buck French said in an interview.

Technically, fans don't buy shares of the 30-year-old Davis. They're buying shares of Fantex Inc., so as the company collects more money, the stock should rise. The stock trades on Fantex's website platform, as opposed to the standard exchanges like the NYSE and NASDAQ.

This is the first time a stock has been linked to the career of a professional athlete.

ESPN.com's Darren Rovell and The Associated Press contributed to this report.